I was accepted to both and chose Western until I was accepted to another school later on.
The reason I chose Western wasn't for educational reasons. I felt that Western and CCOM would provide adequate training although from what I've heard, CCOM has better clinical rotations than Western. CCOM also has better campus than Western. Downers Grove is a much better area than Pomona. But, just outside Pomona is great! Being in Socal is just unbeatable in terms of the weather. I interviewed at CCOM when it was like 23 deg high. I just couldn't picture myself driving 20+ miles various clinical sites during the Chicago winter/snow. That was really a huge deal breaker for me. When I was in Chicago in that cold weather, I realized what I'd have to deal with during my 3rd and 4th yr and decided against CCOM.
But, it appears that DOs are much better known in the midwest than in the west. If this sort of professional recognition is important to you, I'd choose CCOM. I'd also choose CCOM if you don't mind the cold/snow. Cost of living wise, I noticed that Downers Grove was a tad bit cheaper than Southern California. Not by much. But, if you factor in the extra cost for the cold whether, it may even out. Who knows?
All in all, educationally, you likely are going to get better clinical rotations at CCOM. You are likely going to be more comfortable in Socal. Decide from what is important to you.